Electric arc welding is performed in a variety of processes, such as spray welding, globular welding, and short circuit welding. Irrespective of the process employed, an inverter converts three phase line current to the desired voltage or current. An inverter based power supply for electric arc welding has a digitally based control to produce a desired output current or voltage at the arc welding process. In pipe welding, pulse welding or short circuit welding is preferred for the first weld bead, known as the “root pass”, that closes the open gap between edges of adjacent workpieces. For best results, the short circuit electric arc welding procedure is implemented by using the patented STT technology. In this technology, a precise current waveform is outputted by the power supply. Spatter reduction is affected by drastically reducing the current just before the shorted metal separates to create a new arc. Thereafter, the current waveform produces a plasma boost for melting the end of the electrode awaiting the next short. The peak current of the plasma boost pulse is gradually reduced in a current tailout until a set background current is reached. Thereafter, the background current is maintained until the molten metal ball shorts against the workpiece causing the next cycle. In this STT electric arc welding process, the current waveform is accurately controlled by a series of current pulses, the widths of which determine the magnitude of the current at any given time in the waveform. The shape of the waveform is controlled by a waveform generator. By using this technique, the current waveform allows control of the puddle temperature and/or fluidity. Such capability is vital in gap welding applications, such as open root pass in pipe welding. If the puddle is too cold, a lack of metal fusion can result. As a corollary, when the puddle is too hot, a poor internal back bead is possible caused by the weld metal “sucking back” into the root. In the past, STT short circuit welding has been implemented as a current control process. If the operator wants to change heat in the arc and/or puddle, he must adjust current by the machine setting.